Panic in pprust::print_crate from Registry::expand

[reem]

I'm not really sure how to reduce this example, but I am seeing a panic during Registry::expand when using syntex 0.29:

   Compiling google-storage1 v0.1.11+20151229 (file:///Users/reem/code/rust/google-apis-rs/gen/storage1)
failed to run custom build command for `google-storage1 v0.1.11+20151229 (file:///Users/reem/code/rust/google-apis-rs/gen/storage1)`
Process didn't exit successfully: `/Users/reem/code/rust/google-apis-rs/target/debug/build/google-storage1-91992d23db032e43/build-script-build` (exit code: 101)
--- stderr
thread '<main>' panicked at 'assertion failed: (self.right != self.left)', /Users/reem/.multirust/toolchains/nightly/cargo/registry/src/github.com-88ac128001ac3a9a/syntex_syntax-0.29.0/src/print/pp.rs:447
stack backtrace:
   1:        0x109e33e38 - sys::backtrace::tracing::imp::write::h4c3934d94b73ae74jYu
   2:        0x109e35855 - panicking::default_handler::_$u7b$$u7b$closure$u7d$$u7d$::closure.43867
   3:        0x109e35478 - panicking::default_handler::h31854fe07604bc37Ipz
   4:        0x109e2a466 - sys_common::unwind::begin_unwind_inner::hb0e3e92ad83708955Wt
   5:        0x109a55717 - sys_common::unwind::begin_unwind::h13310149087117287422
   6:        0x109c2de40 - print::pp::Printer<'a>::advance_right::h2fd3d40c1346a166N2Z
   7:        0x109c2c08b - print::pp::Printer<'a>::pretty_print::h8b60fbda5e54804cJFZ
   8:        0x109c331b2 - print::pp::break_offset::hb7326f3ba29f680alv0
   9:        0x109c33395 - print::pp::spaces::hb56287ba8248dd6c8w0
  10:        0x109c33422 - print::pp::hardbreak::h8eadc47bce97d74aPx0
  11:        0x109c38431 - print::pprust::PrintState::print_comment::h11066382073331049449
  12:        0x109c367df - print::pprust::PrintState::maybe_print_comment::h13073139524935217014
  13:        0x109c4deee - print::pprust::State<'a>::print_item::h74f5b5971fbec341Fh2
  14:        0x109c3cd2f - print::pprust::State<'a>::print_mod::h500a09ca414ea7159Q1
  15:        0x109c52ff2 - print::pprust::State<'a>::print_item::h74f5b5971fbec341Fh2
  16:        0x109c3cd2f - print::pprust::State<'a>::print_mod::h500a09ca414ea7159Q1
  17:        0x109c3485d - print::pprust::print_crate::h351e124c4e4ef40e1C0
  18:        0x1099f61d3 - Registry::expand::hc5fe903efc538e6fvfa
  19:        0x1098799cc - main::h963dff89d0848740iaa
  20:        0x109e35082 - sys_common::unwind::try::try_fn::h1579330920516057840
  21:        0x109e3338b - __rust_try
  22:        0x109e34f40 - rt::lang_start::h68f017568afbc542Ohz
  23:        0x10988bcf9 - main

the crate in question is the google-storage1 crate from https://github.com/Byron/google-apis-rs.

The panic can be reproduced by cloning the repo and running make storage1-cargo ARGS=build. I believe this to be a bug in syntex, not in google-storage1, but I could be incorrect.

[causal-agent]

Also getting this failure on various google-apis-rs crates, namely google-gmail1.

[Byron]

Please note that the current workaround is to use serde_codegen <= 0.6.13 .
More information can be found in this comment.

[erickt]

Thanks for filing this. This seems to be some bug in the upstream libsyntax. I'll poke around and see if updating syntex to the latest libsyntax will fix things.